The present invention relates to a micro-electro-mechanical system (MEMS) with deflectable actuator plate and a method for producing the same. Further, the invention relates to an electric circuit and an apparatus for transporting a fluid. Further, the invention relates to piezoelectric actuators for MEMS applications.
Micro-electro-mechanical (MEMS) switches could play an important role in future communication systems. In particular ohmic switches are of interest, since the same can be used in a wide frequency range from DC up to several 10 GHz. However, there are only a few commercial applications in niche markets, such as high-frequency measurement technology or the military. They all have in common that they have to be switched almost without power (cold switching) in order to obtain a long life time. Even at low load, due to discharges (arcing), erosion effects will occur at the contact areas up to fusing of the same (cold welding). Soft metals, such as gold, have a particularly strong tendency to fuse, but necessitate only low forces (<50 μN) to obtain a contact resistance of less than 1Ω. Hard metals, such as platinum (Pt) or ruthenium (Ru) are more resistant but necessitate higher forces (>100 μN for 2-3Ω contact resistance). High contact forces up to 1 mN are obtained with electrostatic drives, but at the expense of high voltages (50-150 V). Recently, piezoelectric drives have been examined more and more. The same can generate significant forces at significantly lower voltages, in particular based on lead (P) zirconate (Z) titanate (T)—PZT. The forces obtained by the devices described so far are, however, comparatively low.
Piezoelectrically operated ohmic switches can be implemented as actuators having fixedly cantilevered beam elements, at the movable end of which a contact resides. The beam structure consists of a passive layer with the (active) piezoelectric material thereon (including electrodes). If a voltage is applied to the latter, the same will expand laterally or will contract, depending on the polarity of the applied voltage and the beam warps. In this regard, reference is made to documents [1] and [2].
In MEMS devices having an electrostatic drive, such beam structures are very common, since the same operate well with this drive principle. In the simplest case, a detached metallic beam is pulled against a fixed electrode area by applying a voltage. The resulting force can be transmitted to a contact at the beam end. Piezoelectric beam actuators, however, form a stack of a passive layer and the piezoelectric material (active layer). Due to the expansion or contraction of the active layer at the beam level, analogously to the thermomechanical effect, warping of the actuator structure can be obtained. Here, the generated force is only partly transferred to the contact.
Approaches as known, for example, from US 2002/0074901 try to increase a force of the respective beam elements via lateral interruption of the beam elements and/or to obtain deflections having lower space requirements. However, this necessitates complicated control of the individual beam elements.
Thus, a concept for establishing or releasing a mechanical contact allowing high contact forces and simple control would be desirable.